DESCRIPTION: (Applicant's abstract) The long-term goal of the present project is to determine the structural and functional organization of the retinal ganglion cells with the hope of better understanding the role that these cells play in visual information processing. Recent studies in this laboratory using a ganglion cell-specific monoclonal antibody in combination with various GABAergic makers have identified a previously uncharacterized population of GABAergic ganglion cells in the rabbit retina. A complete characterization of these cells including a determination of their central projection sites in the brain is of great interest in light of recent evidence for the existence of a monosynaptic, inhibitory pathway into the hypothalamus, an area involved in circadian rhythm entrainment. Accordingly, the present study will: i) study the central projection sites of the GABAergic ganglion cells by means of a light microscopic study combining retrograde labelling of ganglion cells with the use of GABAergic markers, ii) define the exact morphology of the GABAergic ganglion cells using retrograde backfill and intracellular labelling techniques in combination with a computerized neuronal reconstruction system and iii) determine the various types of neurotransmitter-specific input to the GABAergic ganglion cells by means of electron microscopic level multiple-label immunocytochemical studies. The development of cell-specific monoclonal antibodies such as the AB5 ganglion cell-specific antibody has provided the means by which the structure, distribution, development, neurochemical specificity and synaptic relationships of a cell population can be studied. The development of such markers for individual ganglion cell subtypes would be an immensely powerful tool for characterizing and studying the functional roles of these structurally distinct subtypes of ganglion cells. Accordingly, the final specific aim of the present study will be to generate new ganglion cell subtype-specific monoclonal antibodies utilizing a novel 'differential immunization' technique. This will involve the use of either cyclophosphamide or neonatal 'tolerization' produces with immunogens obtained from optic nerve transected and normal rabbits. These antibodies can then be used to structurally and functionally characterize these ganglion cell subtype-specific pathways in the retina.